Fix generic type validation for T::Props and composite members

lib/tapioca/runtime/generic_type_registry.rb

@@ -25,11 +25,18 @@ module GenericTypeRegistry
 
       @type_variables = {}.compare_by_identity #: Hash[Module[top], Array[TypeVariableModule]]
 
-      class GenericType < T::Types::Simple
+      # Subclasses `T::Types::Base` rather than `T::Types::Simple` so that all
+      # validation goes through the `valid?` override below. `Simple` fast paths
+      # check `raw_type` directly, which for us is the clone, not the underlying type.
+      class GenericType < T::Types::Base
+        #: Module[top]
+        attr_reader :raw_type
+
         #: (Module[top] raw_type, Module[top] underlying_type) -> void
         def initialize(raw_type, underlying_type)
-          super(raw_type)
+          super()
 
+          @raw_type = raw_type
           @underlying_type = underlying_type #: Module[top]
         end
 
@@ -38,6 +45,24 @@ def initialize(raw_type, underlying_type)
         def valid?(obj)
           obj.is_a?(@underlying_type)
         end
+
+        # @override
+        #: -> String
+        def name
+          T.must(@raw_type.name)
+        end
+
+        # @override
+        #: -> nil
+        def build_type
+          nil
+        end
+
+        # Matches the always-true `<=` we define on the clone in `create_generic_type`.
+        #: (T::Types::Base type) -> bool
+        private def subtype_of_single?(type)
+          true
+        end
       end
 
       class << self

spec/tapioca/runtime/generic_type_registry_spec.rb

@@ -62,6 +62,33 @@ class GenericTypeRegistrySpec < Minitest::Spec
             T.let(SampleGenericInterfaceImplementation.new, SampleGenericInterface[Object])
           end
 
+          it "recognizes underlying-type instances in a composite T::Props member (issue #2130)" do
+            struct_class = T.let(
+              Class.new(T::Struct) do
+                const :members, T::Hash[Symbol, SampleGenericInterface[Object]]
+              end,
+              T.untyped,
+            )
+
+            instance = struct_class.new(members: { key: SampleGenericInterfaceImplementation.new })
+
+            assert_instance_of(SampleGenericInterfaceImplementation, instance.members.fetch(:key))
+          end
+
+          it "recognizes underlying-type instances in a bare T::Props member (issue #2130)" do
+            # A bare (non-composite) member exercises the `T::Types::Simple` setter fast path.
+            struct_class = T.let(
+              Class.new(T::Struct) do
+                const :member, SampleGenericInterface[Object]
+              end,
+              T.untyped,
+            )
+
+            instance = struct_class.new(member: SampleGenericInterfaceImplementation.new)
+
+            assert_instance_of(SampleGenericInterfaceImplementation, instance.member)
+          end
+
           it "does not reuse generic instances for redefined constants with the same name" do
             first_constant, first_generic_type = register_reloadable_generic